Extent Of Lipid Oxidation Research Articles

Effects of ferric chloride on thermal degradation of γ‐oryzanol and oxidation of rice bran oil

The kinetics of γ-oryzanol degradation in antioxidant-stripped rice bran oil were investigated at 180°C for 50 h. Ferric chloride was added to the oil at different concentrations (0, 2.5, 5.0, and 7.5 mg/kg-oil) to determine the degradation reaction rate of γ-oryzanol and the extent of lipid oxidation (peroxide value and p-anisidine value). It was found that the losses of γ-oryzanol and its four components (cycloartenyl ferulate, 24-methylene cycloartanyl ferulate, campesteryl ferulate, and β-sitosteryl ferulate) could be described by a first-order kinetics model. The degradation rate constant, k, linearly increased (p < 0.05) with the ferric chloride concentration, and increased about 1.5 times when 7.5 mg/kg-oil ferric chloride was added. Ferric chloride addition also accelerated the lipid oxidation of rice bran oil significantly (p < 0.05). Practical applications: This paper describes the kinetic analysis of the degradation of γ-oryzanol, a major phytochemical in rice bran oil, at its frying temperature. The results indicated that iron in the form of ferric chloride accelerated both the degradation of γ-oryzanol and lipid oxidation.

Physical Structures in Soybean Oil and Their Impact on Lipid Oxidation

The oxidation of edible oil yields both primary and secondary oxidation products (e.g., hydroperoxides, carbonyls, hydrocarbons, and epoxides), which produce undesirable sensory and biological effects. Consequently, the suppression of lipid oxidation in food matrices is of great importance. The rate and extent of lipid oxidation in many heterogeneous foods are strongly affected by the physicochemical characteristics of water-oil interfaces. This study examined the ability of dioleoylphosphatidylcholine (DOPC) and water to form association colloids within bulk oil, as well as their impact on lipid oxidation kinetics. Attenuation was used to show the DOPC and water concentrations at which association colloids existed without altering the optical properties of the oil. Interfacial tension and fluorescence spectrometry showed the critical micelle concentration (CMC) of DOPC in stripped soybean oil was around 650 μM at room temperature. Small-angle X-ray scattering (SAXS) and fluorescence probes showed that water had a very strong impact on the properties of the association colloids formed by DOPC. Measurement of primary and secondary lipid oxidation products revealed that the association colloids formed by DOPC had a pro-oxidant effect. The characterization of association colloids could provide a better understanding of the mechanisms of lipid oxidation in bulk oils and provide insights into new antioxidant technologies.

Physical and Oxidative Stabilization of Omega‐3 Fatty Acids in Surimi Gels

The objective of the study was to compare the dispersion and oxidative stability of omega-3 fatty acid oil in high- and low-quality surimi gels during 4-mo refrigerated and frozen storage. Low-quality surimi was prepared by subjecting Alaska pollock surimi to 7 freeze-thaw cycles. Surimi gels were prepared with 4% modified starch, 2% salt, and 0.5% or 1% algal DHA or concentrated fish EPA-DHA oil, and stored at -18 or 3 degrees C for 4 mo after being vacuumed packed and pasteurized. The effect of surimi gel properties on oil dispersion was examined using light microscopy equipped with image process software. The extent of lipid oxidation was monitored by thiobarbituric acid reactive substances (TBARS), peroxide value (PV), and fatty acid methly esters (DHA and EPA). Very fine and uniform oil dispersion was observed in the high-quality surimi gel with the average droplet size of 12.37 microm(2) and dispersion of 1.73 x 10(-3) droplets/microm(2) compared to 84.32 microm(2) and 0.57 x 10(-3) droplets/microm(2) in the low-quality gel. Throughout the 4 mo storage, TBARS and PV of high-quality surimi gel were significantly (P < 0.05) lower than those of low-quality surimi gel. The decreases in omega-3 fatty acids in the high-quality surimi gels were lower than those in the low-quality surimi gels under both storage conditions. Results confirm that a highly cohesive gel matrix is required to have a fine dispersion and oxidative stability of omega-3 fatty acids in the surimi gel system. Uniform dispersion and oxidative stability of omega-3 fatty acid oil can be achieved in the highly cohesive surimi gel system without use of antioxidants. This suggests that surimi can be used as a protein-based carrier in developing high omega-3 fatty acids-containing seafood products.

Effect of added citrus fibre and spice essential oils on quality characteristics and shelf-life of mortadella

The objective of this work was to study the effect of adding orange dietary fibre (1%), rosemary essential oil (0.02%) or thyme essential oil (0.02%) and the storage conditions on the quality characteristics and the shelf-life of mortadella, a bologna-type sausage. The moisture, fat, ash content and colour coordinates lightness (L*) and yellowness (b*) were affected by the fibre content. The treatments analysed lowered the levels of residual nitrite (57.56% and 57.61%) and the extent of lipid oxidation, while analysis of the samples revealed the presence of the flavonoids, hesperidin and narirutin. No enterobacteria or psychotropic bacteria were found in any of the treatments. The treated samples stored in vacuum packaging showed the lowest aerobic and lactic acid bacteria counts. Sensorially, the most appreciated sample was the one containing orange dietary fibre and rosemary essential oil, stored in vacuum packaging. Orange dietary fibre and spice essential oils could find a use in the food industry to improve the shelf-life of meat products.

Effect of adding citrus fibre washing water and rosemary essential oil on the quality characteristics of a bologna sausage

There is a growing demand of natural products in human diet, both due to the possible negative effects of synthetic food additives on human health and to the increased consumer perception for this problem in recent years. The aim of this work was to study the effect of adding rosemary essential oil (REO) (200 mg/kg) and different concentrations of citrus fibre washing water (CFWW) (50–100 g/kg), obtained as a co-product during the extraction of dietary fibre from citrus co-products, on the chemical, physical–chemical and sensorial characteristics of a bologna sausage. The moisture content and water activity fell in all the samples compared with the control values. The ash content in formulas added with CFWW and/or REO increased with respect to the control. The addition of CFWW and/or REO had no effect on CIE LAB parameters analysed, pH and textural properties. The samples analysed lowered the levels of residual nitrite and the extent of lipid oxidation. Analysis of the samples revealed the presence of the flavonoids, hesperidin and narirutin. Hesperidin concentrations were higher than narirutin. Sensorially, the most appreciated sample was the one containing 50 g/kg citrus fibre washing water and 200 mg/kg rosemary essential oil.

INFUSION OF PLANT EXTRACTS DURING PROCESSING TO PRESERVE QUALITY ATTRIBUTES OF IRRADIATED CHICKEN BREASTS OVER 9 MONTHS STORAGE AT −20C

ABSTRACT Boneless, skinless chicken breasts were infused with grape seed extract (GSE), green tea extract (GTE), tertiary butylhydroxyquinone and a combination of GTE and GSE. Samples were irradiated and their physicochemical properties were assessed over 9 months of frozen storage (−20C). Irradiation did not affect pH or water-holding capacity. The effect of irradiation on the lightness value, L*, varied depending on storage time and infusion treatment. Irradiation increased redness (P < 0.05) except for samples infused with GTE (3,000 ppm). Irradiation increased maximum shear force, chewiness and hardness (P < 0.05) of cooked samples. Infusion of plant extracts increased lightness and decreased redness (P < 0.05), hardness and maximum shear force. The extent of lipid oxidation in all samples was determined by thiobarbituric acid reactive substances (TBARS) and carbonyl content methods. Irradiation increased both TBARS and carbonyl content in both raw and cooked chicken. Infusion with plant extracts decreased TBARS and carbonyl content compared with controls. PRACTICAL APPLICATIONS Although irradiation is considered a safe and effective means of ensuring the microbial safety of processed meat products, some physicochemical changes occur in the meat after irradiation that negatively affect the preservation of meat quality. Changes such as lipid oxidation and subsequent rancidity can possibly be inhibited with the use of antioxidants. Because of consumer preference for natural versus synthetic additives, natural products that have antioxidant activity could find application in products receiving irradiation treatments. It is the purpose of this study to ascertain the effect of processing with natural antioxidants found in green tea (GTE) and grape seed (GSE) extracts, which contain phenolic compounds such as catechin, epigallocatechin, epigallocatechin-gallate in GTE and procyanidins in GSE, on the physicochemical changes associated with irradiation of raw and cooked boneless/skinless chicken breasts. This preservation technology may find wide application in the meat processing industry as a means of reducing irradiation-induced quality deterioration.

Antioxidant Effects of Berry Phenolics Incorporated in Oil‐in‐Water Emulsions with Continuous Phase β‐Lactoglobulin

AbstractThe purpose of this study was to evaluate the effects of berry phenolics, in this case, black currant (Ribes nigrum) anthocyanins and raspberry (Rubus idaeus) ellagitannins, in the presence of continuous phase β‐lactoglobulin (β‐Lg), on the oxidative stability of Brij 35‐stabilized corn oil‐in‐water emulsions. The extent of lipid oxidation in emulsions was measured by determining the formation of lipid hydroperoxides and hexanal, and extent of protein oxidation by monitoring the loss of tryptophan and cysteine residues in the continuous phase β‐Lg. Berry phenolics at concentration levels of 20 and 50 μM were able to prevent lipid oxidation with and without β‐Lg in the aqueous phase. The results show that a combination of β‐Lg and berry phenolics was more efficient in inhibiting hexanal formation than either component alone. Synergistic effects on antioxidant activity toward hexanal were observed only at the 20 μM levels of berry phenolics in combination with continuous phase β‐Lg. The berry phenolics were also able to inhibit the oxidation of tryptophan and cysteine residues of β‐Lg. The results show that the amino acid residues were oxidized prior to the propagation of lipid oxidation. This suggests that these amino acids were able to inhibit fatty acid scission. The information gained from this study would be useful in protecting emulsion‐based food products from oxidative deterioration.

Effect of the ripening time under vacuum and packaging film permeability on processing and quality characteristics of low-fat fermented sausages

The effect of vacuum ripening of low-fat fermented sausages packaged in films with different permeabilities on their microbiological, physicochemical and sensorial characteristics was studied. High-fat control sausages were produced with 30% initial fat and low-fat sausages with 10% initial fat. The low-fat sausages were separated into: (a) non-packaged (control) and (b) packaged under vacuum on 7th, 12th and 17th day of processing, remaining under vacuum during the ripening period for 21, 16 and 11 days, respectively, in three different oxygen (100, 38 and ⩽ 5 cm 3/m 2/24 h/1 atm) and water vapour (4.5, <2.5 and 1 g/m 2 24 h) permeability plastic bags. Vacuum packaging reduced ( p < 0.05) the weight loss, the hardness and extent of lipid oxidation in the sausages, increased ( p < 0.05) their lightness, but had no effect ( p > 0.05) on the redness, compared to the control sausages. Packaging low-fat fermented sausages under vacuum for the last 11 days of ripening in packaging film with high permeability increased ( p < 0.05) the lactic acid bacteria count. The same product packaged in film with medium permeability had a higher ( p < 0.05) Micrococcaceae count and the same ( p > 0.05) hardness and overall acceptability as the high-fat control sausages. A ripening time of 11 days and the medium packaging film permeability were the most appropriate conditions for the vacuum packaging of low-fat fermented sausages.

Antioxidants in Margarine Emulsions

The lipid oxidation in margarine takes place in continuous liquid oil phase. The extension of fat interfaces in the system – emulsion of water in oil and the dispersion of fat crystals in liquid oil influences on the peroxidation, decomposition of hydroperoxides to aldehydes and the oxidative stability in the comparison with oxidation in the fat blend. Different antioxidants were used in margarine dispersions: &lt;I&gt;L&lt;/I&gt;(+)ascorbic acid, ascorbyl palmitate and DL-&amp;alpha; -tocopherol. Increasing polarity and decreasing molecular size of antioxidants have the positive influence on lipid oxidation: DL-&amp;alpha;-tocopherol is the least effective antioxidant of all antioxidants, ascorbic acid is the most effective antioxidant and ascorbyl palmitate possesses similar, however, lesser effect. The combination of all three antioxidants restricts the production of hydroperoxides, the decomposition of hydroperoxides to aldehydes and the increase of oxidative stability was also achieved. Content of antioxidants 0.02% as ascorbic acid or ascorbyl palmitate mostly restrict the extent of lipid oxidation in the margarine dispersion with existent content of naturally present tocopherols in fat blend.

Solid phase microextraction - gas chromatography for the evaluation of secondary lipid oxidation products in chicken patties during long-term storage

The formation of hexanal, pentanal and malonaldehyde from raw and grilled chicken patties during storage at -18 ºC for 90 days was evaluated by SPME using a DVB/CAR/PDMS fiber. The extraction conditions were optimized to provide reproducible results and avoided fiber saturation even for more oxidised samples. The performance of different DVB/CAR/PDMS fibers was verified during the entire storage period and seven separate fibers were used to assay the extent of lipid oxidation. The relative standard deviation (RSD) was calculated for 60 duplicate analysis and no differences were observed (p > 0.05) among the fibers RSD despite the number of times they were used. The relationship between the different parameters were also established and compared to the results obtained by the traditional TBARS test. Raw patties showed significant (p < 0.05) Pearson's correlations between all parameters, varying from 0.93 to 0.99. However, grilled patties presented a correlation of 0.98 only between hexanal and pentanal.

Effect of hydroxycinnamic acids on lipid oxidation and protein changes as well as water holding capacity in frozen minced horse mackerel white muscle

The antioxidant effectiveness of different hydroxycinnamic acids for inhibiting the formation of off-flavours associated to rancidity in minced frozen horse mackerel white muscle stored at −10 and −18 °C was studied. The influence of lipid oxidation on protein aggregation, protein denaturation and water holding capacity was also determined. Caffeic acid, o-coumaric acid and ferulic acid were the antioxidants tested. The order of antioxidant effectiveness was caffeic acid > ferulic acid > o-coumaric acid accordingly with previous results obtained in chilled horse mackerel. A strong dependence of antioxidant effectiveness to the ratio lipid/antioxidant concentration was observed. There was no evidence to suggest that antioxidants reduce protein aggregation or water holding capacity changes. Protein aggregation was not accompanied by gross protein denaturation, as monitored by differential scanning calorimetry. No evidence was found for a link between extent of lipid oxidation and degree of protein aggregation or water holding capacity changes.

The Role of Degreased Vitis Vinifera Seeds on the Oxidation of Coffee Lipids

The objective of this study was to determine the efficiency of degreased antioxidant used to prevent the oxidation of coffee lipids. The coffee samples in mixture with degreased respectively with regular antioxidant were medium roasted and packed in plastic pouches laminated with aluminum foil. All sets of samples were stored for one year at a medium temperature of 22.5�C. The extent of lipid oxidation was followed by determination of peroxide, acidity and refraction values and by chromatographic analyse of fatty acids content.The results show the advantage of using degreased antioxidant towards regular antioxidant to prevent coffee lipid oxidation.

Effect of pressure and holding time on colour, protein and lipid oxidation of sliced dry-cured Iberian ham and loin during refrigerated storage

Abstract The effect of high pressure (HP) treatments (200 MPa 15 min, 200 MPa 30 min, 300 MPa 15 min, 300 MPa 30 min) on colour, lipid and protein oxidation in sliced vacuum-packed dry-cured Iberian ham and loin during refrigerated storage (90 days, + 4 °C) was evaluated. Pressure level and holding time increased the extent of lipid oxidation in both products. Dry-cured ham showed a higher susceptibility to lipid oxidation than dry-cured loin since HP treatment increased TBA-RS values in dry-cured ham samples while HP treatment decreased TBA-RS values in dry-cured loin samples. However, HP treatment did not affect protein oxidation in both meat products. On the other hand, HP treatment affected instrumental colour since non-pressurized dry-cured meat products showed higher redness than pressurized ones. Regarding changes under storage, after 90 days of refrigerated storage lipid and protein oxidation increased while redness decreased in both HP treated and non-treated dry-cured meat products. Changes induced by HP were only noticeable after HP treatment, as storage reduced the initial differences between HP treated and non-treated samples. Therefore, the lack of differences in long stored dry-cured ham and loin HP treated and non-treated indicates that the application of HP (200–300 MPa/15–30 min) could not affect the quality of dry-cured meat products. Industrial relevance Dry-cured meat products are the meat-based products with the highest sensory quality in Spain and have a high projection in exterior markets. High pressure processing is effective in controlling pathogen and spoilage microorganisms in meat and meat products although it can promote color and oxidation changes that modify sensory characteristics. The study aimed the evaluation of pressure and holding time on color changes and protein and lipid oxidation at vacuum packed slices of Iberian dry-cured ham and loin during subsequent extended chilled storage. High pressure treatment of dry-cured Iberian ham and loin induce changes after treatment although initial differences are not maintained along refrigerated storage.

Effects of Ultra-High-Pressure Homogenization Treatment on the Lipolysis and Lipid Oxidation of Milk during Refrigerated Storage

Free fatty acid (FFA) release and quantification and lipid oxidation extent of ultra-high-pressure homogenized (UHPH) milk samples were evaluated to assess the effect of UHPH on the susceptibility of milk lipids to lipolysis and oxidation. Milk was UHPH-treated at 200 and 300 MPa with inlet temperatures of 30 and 40 degrees C. UHPH-treated samples were compared to high-pasteurized milk (PA; 90 degrees C, 15 s). Results showed that all FFA increased significantly during storage only in 200 MPa samples. Lipid oxidation was measured as an accumulation of lipid hydroperoxides as the primary oxidation product and malondialdehyde and hexanal as the secondary oxidation products. Samples treated at 300 MPa presented higher malondialdehyde and hexanal content compared to 200 MPa treated-samples and to PA milk.

Oxidative Stress, Inflammation and Neutrophil Superoxide Release in Patients with Crohn’s Disease: Distinction Between Active and Non-active Disease

Increased oxidative stress has been previously demonstrated in patients with Crohn's disease (CD). However, to date, this parameter has not been assessed in a comparative study of patients in prolonged remission and those with the active disease. We report here our study of lipid peroxidation, antioxidant and inflammation status in serum derived from 16 active CD patients, 27 clinically stable patients, and 15 healthy controls. Results The extent of lipid peroxidation was higher in CD patients than in the healthy controls, while the levels of lipid peroxides (PD) and of thiobarbituric acid-reactive substances (TBARS) were significantly (P < 0.01) higher in serum obtained from patients with active CD (22 and 30%, respectively) than in that obtained from patients in remission. An analysis of the antioxidant status revealed that the beta-carotene levels in sera derived from all CD patients - patients with active or stable CD (49.4 +/- 15 and 95.6 +/- 25 mg% beta-carotene, respectively) - were higher than that in the controls (145 +/- 40 mg%). Serum activity of glutathione peroxidase (GSH-Px) was significantly (P < 0.001) higher (by 31%) in the patients with active CD than in the control group. There was no significant difference in GSH-Px activity between patients in remission and the controls. In terms of the inflammatory status, we found significantly (P < 0.01) higher levels of C-reactive proteins (CRP) and of tumor necrosis factor alpha (TNFalpha) in patients with active CD than in CD patients in remission. There was a significant correlation between those parameters and the extent of lipid oxidation. Neutrophils, which are a potential source of oxygen-free radicals, were activated by incubation with phorbol myristate acetate (PMA). Superoxide and lysozyme release were significantly reduced in neutrophils derived from patients with active CD (by 25 and 28%, respectively) in comparison to the control group. However, stimulated neutrophils from stable patients demonstrated only a minimally non-significant lower release of superoxide and lysozyme compared to the controls. Conclusion The results obtained in this study demonstrate an enhanced inflammatory and oxidative stress and a decreased antioxidant status in patients with active CD. As the patients improved and became clinically stable, the oxidative parameters decreased, approaching normal values. As neutrophil activation was also lower in patients with active disease, neutrophil activation may represent a possible defense mechanism of the body against tissue injury.

The effect of feeding rosemary, oregano, saffron and &amp;#945-tocopheryl acetate on hen performance and oxidative stability of eggs

In this study the effects of feeding rosemary, oregano, saffron and &#945;-tocopheryl acetate on hen performance and egg quality were investigated. One hundred-twenty Lohmann laying hens, 32 weeks old, were divided into five groups replicated four times with six hens per replicate. One group was given a basal diet and served as control (CON). The experimental diets given to the other four groups were based on the basal diet but contained an additional 200 mg &#945;-tocopheryl acetate/kg (TOC), or rosemary at 5 g/kg diet (ROS), oregano at 5 g/kg diet (ORE) or saffron at 20 mg/kg diet (SAF). At the end of the feeding trial that lasted 56 days, hen performance and some egg quality characteristics were determined, whereas the oxidative stability of the refrigerated stored shell eggs and liquid yolks were also examined. Results showed no significant differences in egg production, feed intake, feed conversion ratio, egg weight and shape, yolk shape, Haugh units and shell thickness among treatments. However, yolk colour was significantly improved in the SAF group compared to all other groups. The extent of lipid oxidation in shell eggs differed among the dietary treatments, but did not change with storage time. In liquid yolk at pH 6.2, lipid oxidation was higher in the CON group compared to all other groups. The ORE group presented lower oxidation rate than the ROS group, but higher than the SAF group, which in turn exhibited higher oxidation rate than the TOC group. When liquid yolk was acidified to pH 4.2, the lipid oxidation profile remained unchanged but the rate was much more intense. Keywords: Rosemary; oregano; saffron; &#945;-tocopherol acetate;egg quality; hen performance; oxidative stability South African Journal of Animal Sciences Vol. 35 (3) 2005: pp.143-151

MEASURING OXIDATIVE STABILITY OF STRUCTURED LIPIDS BY PROTON NUCLEAR MAGNETIC RESONANCE

ABSTRACT The oxidative stability of enzymatically modified oils (structured lipids) and their unmodified counterparts were assessed using proton nuclear magnetic resonance (1H NMR) spectroscopy. This methodology was used to monitor relative changes in the proton absorption pattern of the fatty acids of oils during storage at 60C. Relative changes of aliphatic to olefinic (Rao) and aliphatic to diallylmethylene (Rad) proton ratios during oil oxidation were determined by 1H NMR spectroscopy. An increase in Rao and Rad values was obtained over the entire storage period. The oxidative stability of oils was also evaluated using conjugated dienes (CD) determination, 2‐thiobarbituric acid reactive substances (TBARS) and headspace volatile analysis. A highly significant correlation (r = 0.930–0.992; P ≤ 0.005) existed between the CD values and changes in Rao and Rad during oxidation of all oils. The correlation coefficient between TBARS and changes in Rao and Rad values was in the range of 0.779–0.983 (P ≤ 0.05). A high correlation (r = 0.948–0.996; P ≤ 0.005) was found between hexanal content and Rao and Rad of oils. Propanal content was also highly correlated (r = 0.950–0.990; P ≤ 0.005) with Rao and Rad.PRACTICAL APPLICATIONSAssessment of the extent of lipid oxidation in food is of much interest to producers and scientists alike. Proton nuclear magnetic resonance spectroscopy provides a valuable tool for quantitation of oxidation of food lipids. This procedure was used for evaluating the oxidative state of structured lipids. The procedure is rapid and nondestructive, requires a small amount of material, and may be considered as “green” because it uses a very minimum amount of solvent and is readily applicable to edible oils and oils extracted from food and biological samples.

Influence of flock treatment with the antibiotic tylosin on poultry meat quality: results of a preliminary experiment

The veterinary antibiotic tylosin was administered to broilers at sub-therapeutic and therapeutic levels to study its effect on the quality of poultry breast meat. No statistically significant differences were observed in moisture content, pH, drip loss, colour and extent of lipid oxidation between the breast meat from treated and not treated birds. However, the cooking loss of the meat from the birds administered tylosin was significantly higher than that from the not treated ones. Additionally, the mean shear force of the breast meat was significantly lower for the sub-therapeutically treated broilers than for the not treated and the therapeutically treated ones. It was concluded that the level at which tylosin was administered to the broilers affected the quality of the breast meat, particularly its textural properties.

Mechanisms of Heme Protein-Mediated Lipid Oxidation Using Hemoglobin and Myoglobin Variants in Raw and Heated Washed Muscle

The hemoglobin variant rHb 0.1, which possesses a decreased ability to form subunits, stimulated lipid oxidation in washed fish muscle less effectively as compared to wild-type hemoglobin (rHb 0.0). This could be due to the lower hemin affinity and more rapid autoxidation rate of subunits as compared to tetramers. To differentiate between hemin affinity and autoxidation effects, ferrous V68T Mb was compared to ferrous wild-type myoglobin (WT Mb). WT Mb has a more rapid hemin loss rate (25-fold) than does V68T, while V68T autoxidized more rapidly than did WT Mb (60-fold). Ferrous WT Mb promoted TBARS and lipid peroxide formation more rapidly than did ferrous V68T (p < 0.01). This indicated hemin loss rate was more critical in determining onset of lipid oxidation as compared to autoxidation rate. Hemin alone was capable of stimulating lipid oxidation. Albumin enhanced the ability of hemin to promote lipid oxidation. MetMb promoted lipid oxidation more effectively than did ferrous Mb, which could be due to the lower hemin affinity of metMb as compared to that of ferrous Mb. EDTA, an iron chelator, had no effect on the rate or extent of lipid oxidation mediated by Mb in the cooked system. Variants with a 975-fold range of hemin affinities promoted lipid oxidation with equivalent efficacy in cooked washed cod contrary to results in uncooked washed cod. The cooking temperatures apparently denature the globin and release hemin reactant to such an extent that the impact of hemin affinity on lipid oxidation observed in the raw state is negated in the cooked state. These studies collectively suggest released hemin is of primary importance in promoting lipid oxidation in raw and cooked washed fish muscle.

Phytosterol oxidation in oil-in-water emulsions and bulk oil

Dietary plants sterols (phytosterols) have been shown to lower plasma cholesterol level in humans. Since phytosterols may protect against coronary heart diseases, they are being incorporated into functional foods. However, phytosterols are susceptible to oxidative degradation. The purpose of this study was to evaluate the formation of phytosterols oxidation products (POPs) in oil-in-water emulsions and bulk corn oil. The extent of lipid oxidation was monitored by measuring the lipid hydroperoxides and hexanal, whereas 7-keto derivatives of phytosterols were determined by gas chromatography to follow sterol oxidation. A higher POPs level and formation rate was found in the oil-in-water (o/w) emulsion than in the bulk oil. Interfacial tension measurements showed that phytosterols had a high degree of surface activity, which would allow them to migrate to the oil–water interface of the emulsion droplets where oxidative stress is high.